Electrical cable having a surface with reduced coefficient of friction

ABSTRACT

The present invention includes a cable having reduced surface friction and the method of manufacture thereof including steps in which a conductor wire is coated with a first plastic material and with a mixture of a second plastic material and lubricating material and the coated conductor wire cooled. The cable includes at least one conductor core and at least two coatings of plastic material and incorporates a lubricating material in and/or on the outer layer of plastic material. The equipment for the manufacturing of the electrical cable includes a reel for supplying a conductor wire to an extruding head, which is connected to tanks containing plastic material and lubricating material for coating the conducting wire, and a reel for taking up the cable.

This application claims the benefit of priority of Provisional U.S. Pat.Application No. 60/587,584 filed Jul. 13, 2004, and U.S. patentapplication Ser. No. 10/952,294, filed Sep. 28, 2004 which are hereinincorporated by reference.

The present invention relates to an electrical cable and to a method ofand equipment for reducing its coefficient of friction.

BACKGROUND OF THE INVENTION

Electrical cables which include at least one conductor core and at leastone coating are well known.

Such cables present the disadvantage that their exterior surface has ahigh coefficient of friction, so that they are awkward to fit ininternal sections of walls and ceilings or conduits, since when theycome into contact with the surfaces they become stuck or difficult topull, etc.

In order to overcome said difficulty, alternative materials such asvaselines and the like have been used to coat the exterior surface ofthe cable, thereby reducing the coefficient of friction.

In a complementary manner, guides of small diameter are sometimes used,one end of which is inserted through the cavity through which the cablehas to pass and the other is attached to the end of the cable which mustbe inserted into the cavity. Thus, once the guide has emerged at thedesired place it is pulled until the end of the cable appears againafter having passed through the entire section.

In numerous fields of application, and in particular telecommunications,electric or fiber optic cables are inserted into ducts. There istherefore a need to minimize the coefficient of friction between cablesand the inside walls of ducts.

In one solution, the core of the cable passes via a first extruder whichapplies a conventional sheath thereto i.e., a jacket and/or insulation,often made of polyethylene. The sheathed core then passes through asecond extruder which applies a lubricant layer thereto, such as analloy of silicone resin and polyethylene. The cable lubricated in thatway then passes in conventional manner through a cooling vessel.

A second solution provides for an extruder to cover the core of a cablewith a sheath. At the outlet from that extruder there is disposed acoating chamber for applying granules of material to the still-hotsheath, which granules are designed to become detached when the cable isinserted in a duct. Finally, the coated cable passes through a coolingvessel.

In both of these two prior solutions, it is necessary to interposeadditional equipment between the extruder and the cooling vessel. Thatgives rise to a major alteration of the manufacturing line.

In addition, the equipment for depositing the lubricant must be veryclose to the sheath extrusion head since otherwise it is not possible tocontrol the thickness of the sheath properly. In any event, theadditional equipment occupies non-negligible space and such anarrangement is not favorable for control over the dimensions of thesheath.

Whatever the prior art method used, the manufacture and/or installationof said cables involves a considerable loss of time and an economiccost, since alternative materials are required.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention thus seeks to provide a method for making a cablehaving a surface with reduced coefficient of friction that does notsignificantly alter the geometrical characteristics of the cable and thecable so produced.

The invention thus provides a method for incorporating a lubricant inthe sheath of a cable, the sheath being made by means of an extruder andoptionally followed by a cooling vessel.

In one embodiment of the present invention, the lubricant material ismixed with the sheath material prior to either material being heated.

In another embodiment of the invention, the lubricant material is heatedand mixed with the sheath material prior to the sheath material beingheated.

In a further embodiment of the invention, the lubricant material ismixed with the sheath material after both materials have been heated.

In yet another embodiment of the invention, the non-heated lubricantmaterial is mixed with heated sheath material.

As used herein the term sheath means a jacket and/or insulation appliedto the core of a cable.

DESCRIPTION OF THE INVENTION

With the method and cable of the invention said disadvantages can besolved, while providing other advantages which will be described below.

The method for the manufacture of electrical cables is characterized inthat it includes a step in which a lubricating material is mixed withthe sheath material and this mixture is applied to the core of thecable.

A cable with low coefficient of friction is achieved thereby, so thatsubsequent installation of the same is considerably simplified, since itslides over the surfaces with which it comes into contact.

The step of mixing the lubricating material and the sheath material maybe carried out with the lubricating material heated or not and thesheath material heated or not.

The sheath material normally is introduced in pellet form to an extruderwhich heats and directs the sheath material onto the cable or conductorcore. The present invention includes the embodiment of incorporating thelubricating material into the sheath pellets during the formation of thesheath pellets and introducing this mixture of sheath pellets andlubricant material into an extruder, the embodiment of mixing thelubricant material with the sheath pellets and the embodiment ofintroducing this mixture into the extruder, and introducing the sheathpellets into the extruder and subsequently introducing the lubricatingmaterial into the extruder prior to contacting the cable core.

Advantageously, the lubricant material is selected from the groupconsisting essentially of fatty amides, hydrocarbon oils, fluorinatedorganic resins, and mixtures thereof. The lubricant material may beincorporated at any point in the manufacturing process before theformation of the sheath, and depending upon the material, may be heatedprior to mixing with the sheath material.

In instances where the sheath material has a high melting or softeningtemperature, or for other reasons such as processibility, efficiency ofthe process, etc. the lubricant material may be added to the sheathmaterial as the sheath material is being formed. If the final cableconstruction is such that there are two or more different sheathmaterials applied to the cable core, the lubricant material need only beincorporated into the outermost sheath material.

Advantageous fatty amides and metallic fatty acids include, but are notlimited to erucamide, oleamide, oleyl palmitamide, stearyl stearamide,stearamide, behenamide, ethylene bisstearamide, ethylene bisoleamide,stearyl erucamide, erucyl stearamide, and the like. Advantageoushydrocarbon oils include, but are not limited to, mineral oil, siliconeoil, and the like. Lubricating materials suitable for the presentinvention further include plasticizers, dibasic esters, silicones,anti-static amines, organic amines, ethanolamides, mono- anddi-glyceride fatty amines, ethoxylated fatty amines, fatty acids, zincstearate, stearic acids, palmitic acids, calcium stearate, leadstearate, sulfates such as zinc sulfate, etc., and the like. The abovelubricating materials may be used individually or in combination.

The electrical cable is characterized in that it incorporates alubricating material in the sheath coating, which lubricating materialblooms, migrates toward the exterior, or permeates the cable sheath. Ifdesired the sheath material may be somewhat porous, thereby resulting inthe lubricating material more readily migrating toward the exteriorsurface of the sheath.

The sheath of the cable thus contains sufficient lubricating material toprovide an exterior surface with reduced coefficient of friction.

The equipment for the manufacturing of electrical cables ischaracterized in that it may include a device for the incorporation of alubricating material into the sheath material prior to application tothe cable core.

Said equipment may also include a tank to maintain the lubricatingmaterial, a section for mixing the lubricating material and sheathmaterial and a section for applying the mixture to the cable core.

Moreover, the equipment may also include a pressure adjusting valve(s),a level indicator(s) of the lubricating material tank and sheathmaterial tanks, and a pressure gauge(s).

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, a drawing isattached in which, schematically and by way of example, an embodiment isshown.

In said drawing,

FIG. 1 is a schematic elevation view of equipment for manufacturingelectrical cable, according to the method of the present invention.

FIG. 2 is a section view of a THHN cable of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

THHN or THWN-2 conductors are 600 volt copper conductors with athermoplastic insulation/nylon sheath and are heat, moisture, oil, andgasoline resistant. AWG sizes usually range from 14 through 6. THHNconductors are primarily used in conduit and cable trays for services,feeders, and branch circuits in commercial or industrial applications asspecified in the National Electrical Code. Type THHN is suitable for usein dry locations at temperatures not to exceed 90° C. Type THWN-2 issuitable for use in wet or dry locations at temperatures not to exceed90° C. or not to exceed 75° C. when exposed to oil or coolant. Type MTWis suitable for use in wet locations or when exposed to oil or coolantat temperatures not to exceed 60° C. or dry locations at temperaturesnot to exceed 90° C. Type THHN, THWN-2, and MTW copper conductors areusually annealed (soft) copper, insulated with a tough, heat andmoisture resistant polyvinylchloride (PVC), over which a nylon(polyamide) or UL-listed equivalent jacket is applied.

As can be appreciated in FIG. 1, the equipment 11 for manufacturingelectrical cable 12 of the present invention includes a reel 13 whichsupplies conductor wire 14 to an extruding head 15, which in turnincludes a tank 16 of second plastic material 17; a tank 18 oflubricating material 19 for mixture with plastic material 17 and forapplication onto the exterior surface of the conductor wire 14; acooling box 20 for cooling the exterior surface of the plastic material17—lubricating material 19 mixture which is in a state of fusion orsemi-fusion on the conductor wire or cable core 14; and a reel 21 fortaking up the resulting cable 12. Advantageously the conductor wire iscoated with a first plastic material and this in turn is coated with thesecond plastic material-lubricating material mixture.

As can also be seen in the figures, the tank 18 may include a section 22through which the lubricating material can pass into tank 16 and bemixed with second plastic material 17 and a section 23 through whichlubricating material 19 can be introduced directly into extruding head15 at a point after second plastic material 17 has been introduced intoextruding head 15.

The plastic materials include known materials used in electrical wireand cable products such as polyethylene, polypropylene,polyvinylchloride, organic polymeric thermosetting and thermoplasticresins and elastomers, polyolefins, copolymers, vinyls, olefin-vinylcopolymers, polyamides, acrylics, polyesters, fluorocarbons, and thelike. Advantageously the THHN cable of the present invention has a layerof polyvinylchloride insulation near or adjacent the conductor with anouter layer of polyamide, preferably nylon, or equivalent outer layer.

The present inventive method and the novel cable produced therebyincludes the step of coating conductor wire or cable 14 with the mixtureof second plastic material 17 and lubricating material 19 and optionallycooling the coated cable formed thereby.

Cable 12 is thus obtained with at least one conducting core and anexterior coating, the main characteristic of which is that itscoefficient of friction is low, which makes it easier to install sinceit slips on the surfaces with which it comes into contact.

Another beneficial property gained by the present invention is anincreased resistance to “burn-through.” “Burn-through,” or “pull-by,”results from friction generated by pulling one cable over another duringinstallation, causing deterioration and eventual destruction to its ownjacket as well as the jacket of the other cable. When using a lubricatedcable of this invention the number of six-inch-stroke cycles required toproduce burn-through was increased from 100 to 300.

The present inventive cable may also enhance ease in stripping thejacket from the cable end—termed stripability.

A further benefit of the present invention is the reduction of jacketrippling. Jacket rippling results from the friction of the jacketagainst building materials, causing the jacket material to stretch andbunch. Jacket damage may result. Installation situations, whichrepeatedly caused jacket rippling in unlubricated cable caused norippling in lubricated cable jackets.

Despite the fact that reference has been made to specific embodiments ofthe invention, it will be clear to experts in the subject that thecable, the method and the equipment described can be varied and modifiedin many ways, and that all the details mentioned can be replaced byothers which are technically equivalent without departing from thesphere of protection defined by the attached claims.

For example, cable 12 on which second plastic material 17 andlubricating material 19 are applied can be of any desired configurationand can be an optical fiber cable or the like.

It has been found experimentally that the use of a lubricating materialdisclosed herein is suitable for providing a considerable reduction ofthe coefficient of friction of the cable, which means that it is easierto install without adding any external element to it, which is one ofthe objectives sought in the present invention.

EXAMPLE

To understand the affects of the jacket lubricant system on the ease ofpull variations of the UL (Underwriters Laboratories, Inc.) joist pulltest was utilized.

The joist pull test outlined in UL 719 Section 23 establishes theintegrity of the outer PVC jacket of Type NM-B constructions whensubjected to pulling through angled holes drilled through wood blocks.

The test apparatus consists of an arrangement of 2″×4″ wood blockshaving holes drilled at 15° drilled through the broad face. Four ofthese blocks are then secured into an frame so that the centerlines ofthe holes are offset 10″ to create tension in the specimen through theblocks. A coil of NM-B is placed into a cold-box and is conditioned at−20° C. for 24 hours. A section of the cable is fed throughcorresponding holes in the blocks where the end protruding out of thelast block is pulled through at 45° to the horizontal. The cable is thencut off and two other specimens are pulled through from the coil in thecold-box. Specimens that do not exhibit torn or broken jackets andmaintain conductor spacing as set fort in the Standard are said tocomply.

Pulling wire through the wood blocks provides a more direct correlationof the amount of force required to pull NM-B in during installation.Because of this relationship, the joist-pull test is initially the basisfor which ease of pulling is measured, but a test for quantifying this“ease” into quantifiable data had to be established.

A variable-speed device was introduced to pull the cable specimenthrough the blocks. An electro-mechanical scale was installed betweenthe specimen and the pulling device to provide a readout of the amountof force in the specimen. To create back tension a mass of known weight(5-lbs) was tied to the end of the specimen.

Data recorded proved that NM-B constructions having surface lubricatesreduced pulling forces.

A 12-V constant speed winch having a steel cable and turning sheave wasemployed; the turning sheave maintains a 45 degree pulling angle andprovides a half-speed to slow the rate of the pulling so that more datapoints could be obtained. Holes were drilled in rafters wherebyspecimens could be pulled by the winch.

It was found using this method that lubricated specimens yieldedapproximately a 50% reduction in pulling force when compared tostandard, non-lubricated NM-B specimens. The results are shown in Tables1 and 2 wherein the data was recorded at five second intervals.

TABLE 1 Specimen Description Test Pt. Manufacturer ManufacturerManufacturer Manufacturer Manufacturer Manufacturer Control ControlPresent Descr. A1 A2 A3 B1 B2 B3 1 2 Invention 1st Point 26.8 48.3 37.837.4 16.5 41.9 24 2nd Point 34.6 51.1 35.2 38.1 41.6 42 20.5 3rd Point33.7 46.8 32 33 40.2 38.7 20 4th Point 38.6 49.8 34.7 34.6 41.3 29.517.4 5th Point 33.1 44.8 34.2 32.5 41.3 34.3 20.2 6th Point 28.6 44.732.2 33.2 42.5 35.9 15.8 7th Point 5.5 51 32.2 33.9 41.1 37 17.2 8thPoint 26.8 49.2 33.9 33 40.9 38.4 17.3 9th Point 21.9 52.5 32.6 30.642.7 37.3 21.9 Average 30.51 48.69 33.87 34.03 41.45 37.22 19.37

-   -   AAA—Denotes Outlyers    -   Test in Table 1 performed at a constant speed with winch using ½        speed pulley    -   Test in Table 2 performed on cable with a 5# weight suspended at        building entry    -   Std. Prod.    -   Average Present Invention

37.6289 19.37 TABLE 2 Specimen Description Test Pt. Manufacturer AManufacturer B Control 1 Control 2 Control 3 Invention A Invention BDescr. 14-2 14-2 14-2/12-2 14-2/12-2 14-2/12-2 14-2/12-2 14-2/12-2 1stPoint 34 32.6 50 47.5 40.2 21.5 12.3 2nd Point 35 35.7 50.6 38.3 37.522.9 12.8 3rd Point 35.5 31.2 46.7 43.2 27.5 29 12.1 4th Point 37.7 3544.5 46 36.8 22.4 14.9 5th Point 40.5 30.6 46.2 39.5 36 23.3 11.9 6thPoint 32.9 28.8 40.9 35.7 41.2 21.1 12.5 7th Point 44.2 32.4 52.8 37.537 21.6 11.7 8th Point 43 32.4 40.7 27.7 31.7 22.5 11.7 9th Point 43.430.5 40 31.1 19.2 11 10th Point 40 11.6 Average 38.62 32.13 45.82 38.5035.99 22.61 12.25 14-2/12-2 14-2/12-2 14-2/12-2 Control Avg. Invention AInvention B 40.103241 22.61 12.25

TABLE 3 Pulling Data on THHN Cable Sample Pulling Force, lbs ControlCable 38.5 Cable + 0.25% additive A 18.1 Cable + 0.50% additive A 16.0Cable + 0.85% additive A 18.5 Cable + 0.25% additive B 13.2 Cable +0.50% additive B 10.3 Cable + 0.85% additive B  9.6 Cable + Yellow 77lube 15.3

1. A method for the manufacture of an electrical cable including:providing an electrical conductor wire; providing a first plasticmaterial; coating the conductor wire with the first plastic material;providing a lubricating material; providing a second plastic material;mixing the second plastic material and said lubricating material; andcoating the first plastic coated conductor wire with said mixture of thesecond plastic material and lubricating material.
 2. The method of claim1, wherein the first and second plastic material are in the form ofpellets.
 3. The method of claim 2, wherein the first plastic material ispolyvinylchloride.
 4. The method of claim 2, wherein the second plasticmaterial is a polyamide.
 5. The method of claim 2, wherein thelubricating material is incorporated or mixed with the second plasticmaterial prior to or as the second plastic material is formed intopellets.
 6. The method of claim 1, wherein the lubricating material isintroduced to and mixed with the second plastic material prior tocoating the conductor wire.
 7. The method of claim 1, wherein the stepof coating the conductor wire is accomplished by extruding the mixtureof the second plastic material and lubricating material onto the firstplastic coated conductor wire.
 8. The method of claim 7, wherein amixture of the second plastic material and lubricating material isintroduced into the extruder.
 9. The method of claim 7, wherein thesecond plastic material is introduced into the extruder and thelubricating material is subsequently introduced into the extruder. 10.The method according to claim 1, wherein the lubricating material isselected from the group consisting essentially of fatty amides,hydrocarbon oils, plasticizers, silicone oils and mixtures thereof. 11.An electrical cable including at least one conductor core and at leastone coating of plastic material having a lubricating materialincorporated therein.
 12. An apparatus for the manufacture of anelectrical cable including a reel for supplying a conductor wire to anextruding head, said extruding head connected to a tank containingplastic material for coating the conducting wire, and a reel for takingup the cable, including a device for providing a lubricating material tothe extruding head.
 13. An apparatus for the manufacture of anelectrical cable including a reel for supplying a conductor wire to anextruding head, said extruding head connected to a tank containingplastic material for coating the conducting wire, and a reel for takingup the cable, including a device for providing a lubricating material tothe tank containing plastic material.
 14. A method for manufacturing anelectrical cable, comprising: providing an electrical conductor wire;providing a first plastic material; coating the conductor wire with thefirst plastic material; providing a lubricating material; providing asecond plastic material; mixing the second plastic material and saidlubricating material; coating the first plastic coated conductor wirewith said mixture of the second plastic material and lubricatingmaterial wherein the second plastic material has a temperature of atleast 85° C.; and cooling coated conductor wire.
 15. The method of claim14, wherein during the coating step, the second plastic material has atemperature of approximately 150 degree C.
 16. The method of claim 14,wherein during the cooling step, the second plastic material and thelubricating material are cooled to approximately 20 degree. C.
 17. Themethod of claim 14, wherein the lubricating material is selected fromthe group consisting of fatty amides, hydrocarbon oils, plasticizers,silicone oils and mixtures thereof.
 18. The method of claim 17, whereinthe lubricating material comprises oleamide.
 19. The method of claim 17,wherein the lubricating material comprises erucamide.
 20. The method ofclaim 17, wherein the lubricating material comprises mineral oil. 21.The method of claim 17, wherein the lubricating material comprisessilicone oil.
 22. The method of claim 17, wherein the lubricatingmaterial comprises dibasic esters.
 23. The method of claim 17, whereinthe lubricating material comprises ethylenebisstearamide.
 24. Anelectrical cable comprising an electrical conductor wire coated with afirst plastic material, said first plastic coated conductor wire coatedwith a mixture of a second plastic material and a lubricating material.25. The electrical cable of claim 24 wherein the first plastic materialis polyvinylchloride.
 26. The electrical cable of claim 24, wherein thesecond plastic material is a polyamide.
 27. The electrical cable ofclaim 24, wherein the lubricating material is selected from the groupconsisting essentially of fatty amides, hydrocarbon oils, plasticizers,silicone oils and mixtures thereof.
 28. The electrical cable of claim27, wherein the lubricating material comprises oleamide.
 29. Theelectrical cable of claim 27, wherein the lubricating material compriseserucamide.
 30. The electrical cable of claim 27, wherein the lubricatingmaterial comprises mineral oil.
 31. The electrical cable of claim 27,wherein the lubricating material comprises silicone oil.
 32. Theelectrical cable of claim 27, wherein the lubricating material comprisesdibasic esters.
 33. The electrical cable of claim 27, wherein thelubricating material comprises ethylenebisstearamide.